Electrolytic doping of non-electrolyte layers in printed batteries

ABSTRACT

An electrical or electrochemical cell, c a cathode layer, an electrolyte layer, and an anode layer is disclosed. The cathode layer includes a first material providing a cathodic electric transport, charge storage or redox function. The electrolyte layer includes a polymer, a first electrolyte salt, and/or an ionic liquid. The anode layer includes a second material providing an anodic electric transport, charge storage or redox function. At least one of the cathode and anode layers includes the ionic liquid, a second electrolyte salt, and/or a transport-enhancing additive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/263,711, filed Jan. 31, 2019, now U.S. Pat. No. 10,818,925, which isa divisional of U.S. patent application Ser. No. 15/051,497, filed Feb.23, 2016, now U.S. Pat. No. 10,230,109, which is a continuation of U.S.patent application Ser. No. 13/844,221, filed Mar. 15, 2013, now U.S.Pat. No. 9,276,292, each of which is incorporated herein by reference inits entirety for all purposes.

TECHNICAL FIELD

This disclosure generally relates to electrodes and current collectorsfor electrochemical cells and, more specifically, to improved polymerelectrolyte chemistries and methods of making cells containing theselayers that can be used with devices as single-use or rechargeable powersources.

BACKGROUND

The reduction of electronic device form factors and their power demandshave made it possible to realize new devices that are thin, compact,curved, and flexible. The evolution of portable devices can be, in part,attributed to the combination of the advancements in battery electrodematerials and their compatibility with electrolyte materials. Forexample, the development of more effective high energy density lithiumand lithium-ion electrode materials has enabled portable, compact, highcapacity batteries. The introduction of lithium and lithium-ion solidpolymer and gel electrolytes has relaxed the battery's requirement forrigid and hard packaging, spurring the widespread adoption of thinnerbatteries, hermetically sealed with plastic and foil materials in pouchconstructions. In addition to performance and form factor benefits, theuse of solid-state, polymer, and gel electrolytes have introducedadditional improvements in battery manufacturability, cost, and inherentsafety. Thus, considerable efforts have been dedicated to solid-state,polymer, and gel electrolyte development, as well as coating andprinting fabrication approaches to deposit these electrolytes and theother cell layers.

The demand for thin, miniature, and low-cost batteries has beenpropelled by the increased ubiquity of low power sensors, wirelessdevices, smart cards, wearable devices such as Bluetooth audio devices,headsets, fitness monitors, health monitors, and other devices worn onthe human body. Also, there is continuing interest in developing thinnerphones, tablets, e-readers, and laptops as well as flexible devices suchas flexible OLED displays, flexible memories, and flexible photovoltaicmodules, which may be incorporated in curved or flexible integrateddevices. Even in larger capacity formats, such as in vehicles orairborne applications, thinness, conformability, and flexibility canallow for more efficient use of space, greater robustness, and greatersafety. Such curved or flexible devices would benefit from thinner,conformable, or flexible batteries that have high energy densities, longstorage and operational lifetimes, and cycling capability.

Of the existing battery systems that are being considered for theseapplications, thin-film, lithium polymer, and semi-printed batteries areof interest, though each has shortcomings that have limited theirwidespread adoption. Vapor deposited thin-film lithium and lithium-ionbatteries have relatively low energy storage capacities and powercapabilities due to materials deposition limitations. Lithium polymerbatteries have leveraged the rapid advancements of pouch cell batterymanufacturing, but like thin-film lithium and lithium-ion batteries, areplagued by stringent hermetic encapsulation requirements due to itssensitivity to contamination or corrosion from the environment, fire,and safety issues. There have been recent developments in printablepolymer electrolyte devices that show significant promise for producinghigh energy density, thin, flexible and safe rechargeable batteriesbased on multivalent ion chemistries (PCT/US2011/051469), and that canbe processed by additive coating and printing processes.

This “Description of the Background” section is provided for backgroundinformation only. The statements in this “Description of the Background”section are not an admission that the subject matter disclosed in thissection constitutes prior art to the present disclosure, and no part ofthis “Description of the Background” section may be used as an admissionthat any part of this application, including this section, constitutesprior art to the present disclosure.

Capacity reduction and capacity fade in batteries can be due toinsufficient ionic and ionic transport enhancing species. This isparticularly true in battery cell structures, includingelectrolyte-surrounding layers that have significant fractions ofmaterials that may have some significant solubility, porosity,permeability, and/or diffusivity for ionic species critical forelectrolytic performance. One such battery cell type is the solidpolymer and gel electrolyte ion transport battery, including the lithiumpolymer battery, which may contain electrodes composed of ceramic ormetal particles in a more permeable matrix composed of a polymermaterial, for example U.S. Pat. No. 5,296,318 INTERCALATION BATTERY WITHHYBRID POLYMERIC ELECTROLYTE. Of further interest are printed polymergel-based battery structures such as that disclosed by WO12037171, whichdescribes fully-printed polymer cell constructions and compositions,which can include particle and matrix-based electrodes and currentcollectors, and metal salt and ionic liquid mobile species which canredistribute into electrodes, collectors or packaging. This problem canalso be aggravated by the use of high ionic conducting binders inelectrode formulations, which are used because they can beneficiallyincrease the ion transport, electrochemical reaction kinetics, andutilization in those electrodes, as these promote faster and higherabsolute magnitude species redistribution. An example binder material,which may promote electrode kinetics, but which is susceptible toredistribution of ionic species, is PVDF-HFP (poly(vinylidenefluoride-co-hexafluoropropene)). Note that this redistribution ofspecies can also cause mechanical issues due to volume and stressredistributions associated with the mass transfer. Specifically, thiscan mean increases in volume, pressure, or swelling in the electrodes orcurrent collectors. As ions from the electrolyte redistribute to theelectrolyte-surrounding layers, it also creates a mass loss in theelectrolyte, which can manifest itself as a volume change and/orhigh-stress state, and induce porosity of the electrolyte. The stressstates induced by the mass transfer can result in delaminations, curlingor other mechanical problems. The overall transfer properties of theelectrolyte can also be significantly degraded due to this phenomenon.

In these cases where there is a matrix or active component in anelectrolyte adjacent layer that has some significant solubility or masstransport capability for the ionic species, ionic transport enhancingspecies, buffering agent (organic acids, chelating agents, etc.), orsolvent species in the electrolyte layer, these species can be lost bythe mass transport of those species into the matrix of the electrodes,and from the electrode into the current collector as well viaredistribution during processing, migration, or diffusion. This canoccur during processing, potentially accelerated during subsequenthigh-temperature drying, curing, or forming steps. Redistribution ofthese species into electrolyte adjacent and electrode adjacent layerscan also occur during subsequent printing steps, where a solution or inkthat is applied to the electrolyte or electrode layer may dissolve orinduce the transport of electrolytic species from the electrolyte orelectrodes into the liquid ink, which can contain carriers that may besolvents for the species. Redistribution of the species can also occurduring storage and end-consumer use of the product due to diffusion inresponse to concentration gradient distributions, thermal exposures, orthe application of an electric field, causing ion migration through thebattery.

In general, the unwanted redistribution of these materials can result inlower concentrations of these materials in electrolyte or electrodelayers, leading to degraded performance due to increases inelectrochemical impedance, loss in capacity, and/or loss in highrate-handling capacity. This can happen immediately after processing, orit can lead to performance fade or loss over time and/or use as thespecies continue to redistribute in the cell structure.

FIG. 1 shows discharge capacity data (1 cm2 active area, 100 microampsconstant current charge and discharge) for a series of printed batterysamples after different storage periods (room ambient conditions) beforetesting. The cells were printed in a top cathode structure with ionicpermeable cathode matrix materials and ionic permeable current collectorbinders. Electrolyte and cathode formulations followed the proceduredisclosed in WO12037171, and the top cathode current collector wascomposed of a mixture of graphite, acetylene black, and a polyvinylidenefluoride-based copolymer. The electrolyte formulation can demonstrateionic conductivities over 10{circumflex over ( )}-3 Ohm-cm in impedancemeasurements. For the completed cells in this experiment, thesignificant capacity fade was observed with longer storage timeintervals out to ^(˜)1 month storage time. The electrolyte, cathode, andcurrent collector contained ionic liquid and metal salt-solvatingpolymers. The cathode electrode and the current collector had acomposite structure with continuous percolation paths of polymer thatinterconnect, and that would allow ionic liquid and metal salt molecularand ionic drift, or migration or diffusion through their structures.

After the 1 month storage and test cycle, cells from this fabricationlot were then exposed to ionic liquid and ionic liquid+zinc saltmixtures, such that ionic species could diffuse through the currentcollector and cathode and into the cathode and electrolyte layers. Thisresulted in a significant increase in capacity for the exposed samplesversus control, non-exposed samples (see FIG. 2 and FIG. 3). Thisimprovement in measured capacity is consistent with the diffusion ofionic liquid and metal salt through the current collector and cathodeinto the electrolyte layer, where it enhances ionic conductivity in thecathode and electrolyte and increases effective cell capacity. Some ofthe reduction in capacity observed over time in FIG. 1 may be associatedwith ionic transport of species out of the electrolyte and electrolytecathode interfacial areas into the current collector, resulting inreduced ionic conductivity in these layers.

Additional experiments with subsequent printed layers of printedconductors and electrolytes show the specific interactions between anionic liquid+metal+salt+PVDF-HFP layer and a conductiveparticle+PVDF-HFP layer. Samples were prepared by stencil printing aconductive pattern of PVDF-HFP+Ni particle ink, drying the printed ink,and subsequently stencil printing and drying an ionicliquid+metal+salt+PVDF-HFP layer on top of the Ni particle-containingink pattern in the following configuration and measuring the end-to-endresistance. This experiment showed that the resistance of the nickellayer increased significantly immediately after the electrolyte wasprinted on top of the nickel current collector bar, and that theconductivity continued to rise over time, on the scale of hours, afterthe electrolyte was dried, indicating that liquid phase redistributionand longer term, solid phase diffusion effects can be active when thesetypes of electrolyte interact with adjacent layers. Additionalexperiments with exposure of particle+binder conductors to neat ionicliquid showed a similar resistance increase. Further experiments withmethacrylate binder-based nickel particle conductors, which show littletendency to swell with exposure to electrolyte materials, showedsubstantially reduced resistance changes for printed conductors incontact with ionic liquid. The conductivity loss mechanism is likelydominated by swelling of the binder of the conductive layer with theionic liquid and/or metal salt from the electrolyte. This swelling ofthe conductive layer due to diffusion, drift, migration, orredistribution during deposition of electrically active species out ofthe electrolyte and/or electrolyte cathode interfacial areas and intothe current collector, results in the observed reduction in ionicconductivity.

For the structure 10 in FIG. 4, the components, compositions, andprocessing conditions are as follows

-   -   Printed nickel bar 12 dimensions: 1 cm×8 cm    -   Printed electrolyte bar 14 dimensions: 1 cm×2.5 cm    -   Nickel ink: Strem Ni powder+Arkema PVDF-HFP+Sigma Aldrich NMP    -   Ni Drying: 30 minutes @ 60° C.    -   Nickel to binder weight ratios were as follows:        -   1. PVDF-HFP:Ni=1:9        -   2. PVDF-HFP:Ni=1:12        -   3. PVDF-HFP:Ni=1:14    -   Electrolyte ink: Merck BMIM triflate+zinc triflate+Arkema        PVDF-HFP+Sigma Aldrich NMP (following WO2012/037171 A2)    -   Electrolyte Drying: 2 hrs @ 60° C.

The following table shows end-to-end resistance measurements for thecomposition variants in the printed Ni/Printed electrolyte experimentversus time after electrolyte layer printing and drying:

PVDF-HFP:Ni PVDF-HFP:Ni PVDF-HFP:Ni Ratio by weight Ratio by weightRatio by weight Hours 1:9 (ohm) 1:12 (ohm) 1:14 (ohm) 0 385 186 194 1483 300 476 2 2625 1212 1264 18 8118 7227 735 21 2540000 3460000 2050000138 Overload Overload Overload

Prior to electrolyte deposition, the resistance of the printed Niconductors measured end-to-end varied from 23.4 to 24.5 ohms.

SUMMARY

A first aspect of the present disclosure concerns an electrochemicalcell, comprising a cathode layer, an electrolyte layer, and an anodelayer. The cathode layer comprises a first material providing a cathodicelectric transport, charge storage, or redox function. The electrolytelayer comprises a polymer, a first electrolyte salt, and the ionicliquid. The anode layer comprises a second material providing an anodicelectric transport, charge storage or redox function. At least one ofthe cathode layer and the anode layer further comprises the ionicliquid, a second electrolyte salt, and/or a transport-enhancingadditive. Each of the cathode layer, electrolyte layer, and anode layermay include the ionic liquid, electrolyte salt and/ortransport-enhancing additive in a concentration at or near a saturationconcentration. In one example, the “saturation concentration” can meanthe concentration beyond, which increases in concentration result in thepresence of significant quantities of undissolved or separatedmaterials. Alternatively, “saturation concentration” can mean theconcentration beyond which no additional beneficial effect of theincreased component occurs with an increase in the concentration of thatcomponent. In some cases, exceeding concentration limits that result information of large or appreciable quantities of separated liquid (e.g.,an added ionic liquid, solvent, or ionic liquid-salt mixture) can bedetrimental, as this can lead to enhanced dendrite formation in thoseareas, destabilization of interfaces, delamination, and surface wettingissues. In a further alternative, “saturation concentration” can meanthe maximum concentration of a particular component in a given layerunder the conditions of manufacture and/or use. In one embodiment, theconcentration of the ionic liquid in each of the cathode layer,electrolyte layer, and anode layer is substantially at the saturationconcentration.

In some embodiments, the cathode layer comprises the second electrolytesalt, and the anode layer comprises a third electrolyte salt. The first,second and third electrolyte salts may be identical to or different fromone or more of the other electrolyte salts. For example, the first,second, and third electrolyte salts may each have a common ion (e.g.,Zn²⁺ or trifluoromethanesulfonate). The cathode layer and/or anode layermay further include the transport-enhancing additive, which can be asupporting solvent for improving ionic conductivity such as ethylenecarbonate, propylene carbonate, etc.

In some embodiments, the electrochemical cell may further comprise afirst current collector layer on the cathode layer, and a second currentcollector layer on the anode layer. The first and second currentcollector layers generally comprise an identical or different conductivematerial. In further embodiments, each of the first and second currentcollector layers further comprises the ionic liquid. In addition, eachof the first and second current collector layers may further comprise anidentical or different electrolyte salt, and each of the electrolytesalts in the electrochemical cell may have a common ion. The firstand/or second current collector layers may further include thetransport-enhancing additive. The cathode layer, anode layer and/or thefirst and/or second current collector layers may further include adesiccation agent such as SiO₂ or one or more fillers to improvemechanical stability.

In some embodiments, the ionic liquid content of the electrolyte layer,an electrode layer, or a current collector layer may be below thesaturation limit and/or the concentration of the ionic liquid in anotherlayer (e.g., the electrolyte layer), relative to the total solid contentin the layer or as a ratio to the (primary) polymer content in the layer(e.g., the electrolyte layer or film). In other embodiments, the ionicliquid content of the electrolyte layer, electrode layer, or currentcollector layer may be the same as the concentration of the ionic liquidin another layer (e.g., an electrode layer and/or current collectorlayer), relative to the total non-impermeable material content or thenon-impermeable-to-ionic liquid material ratio in the electrolyte layer,or as a ratio to the (primary) polymer content in the electrode layer(s)or current collector layer(s).

In some embodiments, the electrolyte salt content of the electrolytelayer, an electrode layer or a current collector layer may be below thesaturation limit and/or the concentration of the electrolyte salt inanother layer (e.g., the electrolyte layer), relative to total the solidcontent in the layer or as a ratio to the (primary) polymer content inthe layer (e.g., the electrolyte layer or film). In other embodiments,the electrolyte salt content of the electrolyte layer, an electrodelayer or a current collector layer may be the same as the concentrationof the electrolyte salt in another layer (e.g., an electrode layerand/or current collector layer), relative to the total content ofmaterials not impermeable to the electrolyte salt in the electrolytelayer, or as a ratio to the (primary) polymer content in the other layer(e.g., the electrode layer[s] or current collector layer[s]). In somefurther embodiments, the electrolyte salt content or ionic liquidcontent in the electrode layer(s) and/or current collector layer(s) maybe higher than the corresponding content in the electrolyte layer, toserve as a positive diffusion source of the electrolyte salt or ionicliquid.

Some embodiments may also include one or more solvents, additives, orother materials having ion transport-enhancing properties; one or morebuffers or chelating agents in an electrode and/or current collectorlayer that act as diffusion blockers or diffusion sources for flow ofthese materials from the electrolyte layer or adjacent electrode orcurrent collector layers.

The first conductor may comprise a conductive compound, conductivecarbon, or a combination thereof. The polymer may comprise apolyfluoroalkene, such as a polymer or copolymer of a fluoroalkene ofthe formula C_(x)H_(y)F_(z), where x is an integer of from 2 to 6, z isan integer of from x to 2x, and y+z is an even integer of from x+2 to2x. The ionic liquid may comprise an imidazolium salt, pyrrolidiniumsalt, ammonium salt, pyridinium salt, piperidinium salt, phosphoniumsalt, or sulfonium salt that is a liquid at ambient or room temperature.The electrolyte salts may release cations selected from the groupconsisting of zinc ions, aluminum ions, magnesium ions, and yttriumions, and anions selected from the group consisting of chloride,tetrafluoroborate (BF₄ ⁻), trifluoroacetate (CF₃CO₂ ⁻),trifluoromethanesulfonate (CF₃SO₃ ⁻), hexafluorophosphate (PF₆ ⁻),bis(trifluoromethyl-sulfonyl)amide (NTf₂ ⁻), andbis(fluorosulfonyl)imide (N(SO₂F)₂)⁻. The second conductor may comprisean elemental metal or an alloy thereof, a carbon-based material, and/ora conducting polymer.

In a further aspect, the present disclosure concerns a method of makingan electrochemical cell, comprising forming a cathode layer on asubstrate, forming an electrolyte layer on the cathode layer, andforming an anode layer on the electrolyte layer. The cathode layer,electrolyte layer, and the anode layer are as described herein. Each ofthe cathode layer, electrolyte layer, and anode layer may include theionic liquid and/or the electrolyte salt in a concentration at or near asaturation concentration.

In some embodiments, forming the cathode layer comprises printing an inkcomprising the first conductive material or a precursor thereof, dryingand/or curing the first conductive material or precursor thereof to forma cathode, and contacting the cathode with the ionic liquid to dope orimpregnate the cathode with the ionic liquid. Forming the electrolytelayer may comprise printing an ink comprising the polymer, the firstelectrolyte salt, and the ionic liquid on the cathode layer, and formingthe anode layer may comprise printing an ink comprising the secondconductive material or a precursor thereof on the electrolyte layer,drying and/or curing the second conductive material or precursor thereofto form an anode, and contacting the anode with the ionic liquid to dopeor impregnate the anode with the ionic liquid. In one embodiment, thecathode layer is printed on a substrate. Alternatively, the anode layeris printed on the substrate, the electrolyte layer may be printed as anelectrolyte ink on the anode layer, and the cathode layer is printed onthe electrolyte layer.

The method may further comprise forming a first current collector layeron the cathode layer (or vice versa), and forming a second currentcollector layer on the anode layer (or vice versa). The first and secondcurrent collector layers may comprise the same or different conductivematerial as the other current collector layer and/or the cathode oranode. In further embodiments, each of the first and second currentcollector layers further comprises the ionic liquid and/or electrolytesalt, and the concentration of the ionic liquid and/or electrolyte saltin each of the cathode layer, electrolyte layer, and anode layer issubstantially at the saturation concentration.

In other embodiments, the ionic materials, solvents, iontransport-enhancing additives and/or other beneficial species may beintroduced to the cell from an external liquid or solid source. Thissource could be temporary, such as through immersion in a liquid, or byphysical contact with an external source. Alternatively, the sourcecould be a permanent donor layer, such as a layer that forms part of thepackaging of the device.

In other embodiments, the ionic materials may be redistributed in thecell structure through the application of one or more electric fieldsbetween the electrodes, electrolytes, and/or current collectors.Alternatively, an external donor layer (such as a layer that forms partof the packaging of the device) that does not have a primary function asan electrode or collector of current can be used to apply such anelectric field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the discharge capacities of printedZinc/polymer electrolyte/MnO₂/C collector cells after various storageintervals in air.

FIG. 2 is a graph showing discharge capacity versus charge/dischargecycles for control cells (no post-fabrication ionic exposure) after the1 month aging experiment in FIG. 1, and corresponding cells that wereexposed to ionic liquid and ionic liquid+zinc metal salt.

FIG. 3 is a graph showing voltage discharge curves for control cells (nopost-fabrication ionic exposure) after the 1 month aging experiment inFIG. 1, and corresponding cells that were exposed to ionic liquid andionic liquid+zinc metal salt.

FIG. 4 depicts the structure of an exemplary cell on which experimentswere performed to show the specific interactions between an ionicliquid+metal+salt+PVDF-HFP layer and a conductive particle+PVDF-HFPlayer.

FIGS. 5(A)-(B) respectively show a diagram of the layers in an exemplarycell (FIG. 5(A)) and a photograph of an actual cell (FIG. 5(B)).

FIG. 6 is a cross-sectional diagram showing an exemplary zinc poly-typecell structure in which only the electrolyte layer is doped with anionic liquid and working ion salt (e.g., Zn triflate).

FIG. 7 is a cross-sectional diagram showing stress states due to massflow from IL or salt diffusion from the electrolyte layer to theadjacent layers in the device.

FIG. 8 is a cross-sectional diagram showing a cell structure with aconstant ionic liquid and salt doping structure throughout thestructure.

FIG. 9 is a graph showing the cycle fade of discharge capacity forprinted battery cells with increasing cathode IL and salt doping fromleft to right.

FIGS. 10(A)-(B) are graphs showing the first cycle discharge capacity(FIG. 10(A)) and the third cycle discharge capacity (FIG. 10(B)) at 300μA constant current for the experimental variants listed in Table 6below. Cells were charged at 300 μA current to 1.8V, and then heldpotentiostatically at 1.8V until the cell current dropped below 50 μAprior to discharge.

FIG. 11 is a graph showing discharge voltage curves with higher averagevoltages for the Series 400 doped anode and doped cathode cell(9125_0401_0005_0002) versus the Series 300 undoped cell(9125_0301_0004_0002).

FIG. 12 is a plot of discharge capacity versus discharge current forsets of cells from the experiment(s) described in Table 5 below.

DETAILED DESCRIPTION

Various embodiments are illustrated in the context of a printable zincelectrochemical cell, in which divalent ions travel through a gelelectrolyte. The skilled artisan will readily appreciate, however, thatthe materials and methods disclosed herein will have application in anumber of other contexts where divalent or monovalent ion transport isapplicable or desirable, and that other systems (based on monovalent ordivalent ion transport, or other ion transport systems of highervalency) are also suitable for use in the present disclosure. Thisdisclosure applies to structures, which are deposited on foils, plasticsubstrates, fabrics (woven and nonwoven), and papers, as well as incases where underlying and overlying elements have barrier properties tothe outflow of cell species. This disclosure may be particularly usefulin cases where these elements are not impermeable to electrolyticspecies.

In this disclosure, the terms “negative electrode” and “anode” are usedinterchangeably, and the use of one term generally includes the other,but both terms may be used to mean “anode.” Likewise, the terms“positive electrode” and “cathode” are used interchangeably, and the useof one term generally includes the other, but both terms may be used tomean “cathode.”

In this disclosure, the term “current collector” refers to a conductiveelement in contact with the anode or cathode.

FIG. 5(A) is an exemplary cross-sectional diagram of an electrochemicalcell according to an embodiment of the disclosure. The cell comprises acathode (1) and anode (2) separated by an electrolyte layer (3). As isalso shown in FIG. 1, current collectors (4) may be positioned at theopen sides of the anode (2) and the cathode (1) to provide properelectrical contact with a load applied to the current collectors. Insome cases, it is also possible that an electrode also serves as acurrent collector, as could be the case with a highly conductivecomposite electrode or an electrode foil with sufficient conductivity.Conductivity for a current collector or combined current collector andelectrode would be <100 ohm/sq preferably <10 ohm/sq, most preferably <1ohm/sq). It is appreciated that the current collectors (4) are anoptional component, and the cell may comprise other configurations interms of vertical ordering of the stack (i.e., anode on bottom andcathode on top). FIG. 5(B) shows a scanning electron image of acryogenically-fractured cross-section of a printed cell stack followingWO2012/037171 A2, which is an example structure to which this disclosurecan be applied. The center darker layer is the electrolyte layer, whichis sandwiched by a Zn-based anode (top) and an MnO₂-based cathode layer(bottom).

In FIG. 5(B), it can be clearly seen that the anode and cathode can beconsiderably thicker than the electrolyte. This particular stackincludes an electrolyte with a triflate-based ionic liquid and workingmetal salt in a PVDF-HFP mixture, a cathode that comprises or consistsessentially of a mixture of PVDF-HFP, MnO₂ particles and carbonconductive additive, and an anode that comprises or consists essentiallyof zinc particles in PVDF-HFP. Top current collectors on this stackinclude conductive carbon, graphite, and Ni in a polymer binder, or alaminated foil (e.g., a conductive metal, alloy, or metal compound filmon a metal or alloy foil, such as nickel, copper, titanium, aluminum orstainless steel foil). The current collectors are not shown in FIG. 6,but are similar in configuration to the anode layer (e.g., Ni particlesin an PVDF-HFP binder) in another exemplary cell. In this particularcase, all materials were deposited by sequentially dispensing and dryinglayers of liquid solutions in the volatile solvent n-methylpyrolidone(NMP). Based on the fact that (i) the electrolyte layer was deposited asa wet layer dissolved in NMP, which is also a solvent for the PVDF-HFPin the cathode layer, and (ii) there was significant thermal processingafter the electrolyte was deposited, there is a driving force fortransport of ionic liquid (IL) and salt out of the electrolyte layerinto the electrodes and collectors, since those other layers hadnegligible IL or salt concentration as deposited. On the other hand,there was an equivalent solubility in the respective binders as there isin the electrolyte. Thus, it can be concluded that IL and salt diffuseout, drifts, migrates, and/or redistributes from the electrolyte layerduring or after processing into the adjacent layers, resulting in anincrease in IL and salt concentrations in the other layers and areduction in the concentrations of IL and salt in the electrolyte layer.This movement of IL and/or salt may cause short term effects or beresponsible for longer-term shifts in ionic conductivity and batteryperformance after fabrication.

As stated above, the suppression of transport of the ionic liquid andelectrolyte salt out of the electrolyte can help maintain a higherfraction of the electrolyte's starting concentration of ionic liquid,thus stabilizing ionic conductivity-related kinetics changes andcapacity loss. Suppressing this ionic liquid and electrolyte salttransport loss may also prevent the formation of porosity in theelectrolyte layer and film stresses related to mass loss from theelectrolyte layer, which in turn can lead to poor performance,delamination, and other losses.

Furthermore, additional experiments showed that printing of dopedelectrolytes over conductive layers formed from conductive particles,including nickel and carbon in PVDF and PVDF-HFP causes a permanentreduction in the conductivity of the underlying conductive layer whileprinting non-doped PVDF over these same conductors did not permanentlyaffect the conductivity. This further supports the hypothesis that ionicliquid (IL) and/or electrolyte salt transfer from electrolyte layersinto adjacent layers is a reasonable explanation of this behavior. TheIL and/or electrolyte salt may pass into the binder of the conductiveadjacent layer causing the reduced conductivity, possibly throughswelling and loss of conductive contact between particles in theconductive layer. Note that such swelling and mass loss from theelectrolyte could also cause other detrimental effects, including lossof ionic conductivity in the electrolyte, porosity in the electrolytelayer, particle release from the cathode into the electrolyte layer, anddelamination of the electrolyte layer.

To solve the above problems, the ionic liquid and salt, or moregenerally, any dissolved additive in the electrolyte, can also beincluded in the formulation of the adjacent electrodes or currentcollectors, thus suppressing diffusional losses from the electrolyte andpreventing swelling of the electrodes and electrolytes.

Example embodiments balance the current IL+electrolyte salt doping levelin the electrolyte with the PVDF HFP content in each of the layers.Formulations for the doping level in the electrodes (or collectors) maybe such that the metal salt or ionic liquid concentration is lower thanin the electrolyte (or electrode), but preferably, the electrode (orcollector) doping level matches or exceeds the doping level in theelectrolyte itself to block diffusion and perhaps to provide a source ofdopant to the electrolyte layer. In cases where the active or conductiveparticles in the electrode or collector ink are impervious to the ionicdopants to be added, the doping level for the electrode or collector inkwould be calculated factoring in only the ionic permeable parts of theelectrode or collector. Impermeable materials and inclusions areessentially inert for the purpose of this calculation and do notrepresent a sink or source of dopants, except in instances where suchmaterials or inclusions may be porous or of high surface area.

Example formulations of electrolytes and current collectors are givenbelow in Tables 2 and 3. Molarities of ionic liquid and zinc salt(considering only the fraction of the volume that contains Ionic Liquidand zinc soluble materials) can vary from 10{circumflex over ( )}−1 M to5M (for either component or a composite mixture).

TABLE 2 Example Electrolyte Formulations Electrolyte Formulation 1Formulation 2 Zn Triflate (OTf) [g] 1.125 2.9234 BMIM OTf [g] 8 8PVDF-HFP [g] 8 8 Zn OTf [wt %] 0.066 0.171 BMIM OTf [wt %] 0.467 0.467PVDF-HFP [wt %] 0.467 0.467 Zn OTf [vol %] 2.3% 5.8% BMIM OTf [vol %]56.9% 54.9% PVDF-HFP [vol %] 40.8% 39.3% Zn OTf [M] 2.8E−01 7.1E−01 BMIMOTf [M] 2.5459 2.4545

Note that the electrolyte examples here represent one case. Advantageousformulations could also contain solvents, polymers, and other additives,which may replace the ionic content or the PVDF-HFP. Current collectorformulations are generally based on ^(˜)70% conductor loading by volume,but lower percentages may also be possible, as well as composites ofdifferent metals, carbon, graphites, CNT, graphene, etc., to create arobust and effective conductor. The same calculations can also be donefor a simple anode, such as a Zn powder-based printed anode layer, usingthe densities of Zn and appropriate binders and/or additives. A similarcalculation can be performed for the cathode, substituting, for example,the densities and molecular weights of MnO₂ and adding a set of fieldsand data for conductive additives, such as carbon AB and graphite, whichcan be used in cathode formulations. One feature of these formulationcalculations is that they maintain the same concentrations of ionicspecies in the electrolyte and in other layers in the battery.

TABLE 3 Example Current Collector Formulations Current CollectorFormulation 1 Formulation 2 Zn OTf [g] 1.125 2.9234 BMIM OTf [g] 8 8PVDF-HFP [g] 8 8 Nickel [g] 198 206 Zn OTf [wt %] 0.005 0.171 BMIM OTf[wt %] 0.037 0.467 PVDF-HFP [wt %] 0.037 0.467 Nickel [wt %] 0.920 0.958Zn OTf [vol %] 0.007 0.017 BMIM OTf [vol %] 0.171 0.164 PVDF-HFP [vol %]0.122 0.118 Nickel [vol %] 0.700 0.700

Example polymers that have a finite solubility for ionic, electrolytic,solvating, or ion transport-enhancing species in the electrolytes,electrode binders, and collector binders include: polyvinylidenefluoride and its copolymers, polyanilines, polyethers, polyethyleneoxides, polyimides, polyacrylates, polyacrylic copolymers, polyesters,polyester copolymers, polyvinylidene chlorides, etc.

Example mobile ionic species that may be in electrolytes and that candiffuse out include cation and anion combinations including the cations:imidazolium, pyrolidinium, tetraalkyl amines, Li, Zn, Na, Al, and Mg,the anions: trifluoromethane-sulfonate (triflate), bis((trifluoromethyl)sulfonyl)imide (triflate sulfimide, or TFSI),hexafluorophosphate, borate, and cation-anion pairs such as ionicliquids and metal salts. Specific mobile ionic species include compoundssuch as:

-   1-butyl-3-methylimidazolium trifluoromethanesulfonate,-   1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide,-   1-butyl-3-methylimidazolium hexafluorophosphate,-   1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide, and-   1-butyl-3-methylimidazolium tetrafluoroborate;-   1-Butyl-2,3-dimethyllimidazolium trifluoromethanesulfonate,-   1-Butyl-2,3-dimethyllimidazolium    bis((trifluoromethyl)sulfonyl)imide,-   1-Butyl-2,3-dimethyllimidazolium hexafluorophosphate,-   1-Butyl-2,3-dimethyllimidazolium    bis((trifluoromethyl)sulfonyl)amide, and    1-Butyl-2,3-dimethyllimidazolium tetrafluoroborate;-   1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate,-   1-butyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide,-   1-butyl-1-methylpyrrolidinium hexafluorophosphate,-   1-butyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)amide,    and-   1-butyl-1-methylpyrrolidinium tetrafluoroborate;-   1-butyl-1-methylpyridinium trifluoromethanesulfonate,-   1-butyl-1-methylpyridinium bis((trifluoromethyl)sulfonyl)imide,-   1-butyl-1-methylpyridinium hexafluorophosphate,-   1-butyl-1-methylpyridinium bis((trifluoromethyl)sulfonyl)amide, and-   1-butyl-1-methylpyridinium tetrafluoroborate;-   1-Ethyl-1-methylpyrrolidinium trifluoromethanesulfonate,-   1-Ethyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide,-   1-Ethyl-1-methylpyrrolidinium hexafluorophosphate,-   1-Ethyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)amide,    and-   1-Ethyl-1-methylpyrrolidinium tetrafluoroborate;-   1-Ethyl-3-methylimidazolium trifluoromethanesulfonate,-   1-Ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide,-   1-Ethyl-3-methylimidazolium hexafluorophosphate,-   1-Ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide, and-   1-Ethyl-3-methylimidazolium tetrafluoroborate;-   1-methyl-1-propylpyrroldinium trifluoromethanesulfonate,-   1-methyl-1-propylpyrroldinium bis((trifluoromethyl)sulfonyl)imide,-   1-methyl-1-propylpyrroldinium bis(trifluoromethylsulfonyl)amide,-   1-methyl-1-propylpyrroldinium hexafluorophosphate, and-   1-methyl-1-propylpyrroldinium tetrafluoroborate; and-   zinc bis((trifluoromethyl)sulfonyl)imide,-   zinc trifluoromethanesulfonate,-   zinc bis((trifluoromethyl)sulfonyl)amide,-   zinc tetrafluoroborate,-   zinc hexafluorophosphate,-   zinc nitrate, and-   zinc chloride.

Example solvating or ion transport-enhancing species that may be presentin the electrolyte or electrodes and that may diffuse out includematerials and/or solvents such as: carbonates such as ethylene carbonateand propylene carbonate, glycols such as ethylene glycol, diethyleneglycol, polyethylene glycols, propylene glycol and oligomers thereof,ethylene oxides, propylene oxides, polymers and copolymers of ethyleneand propylene oxides, ethers, fluorinated carbonates, fluorinatedethers, and block copolymers of the previously listed (polymerizable)materials. Other high boiling point solvents (including polar solventshaving a boiling point at 1 atm of >150° C., >200° C., or >250° C.), canalso be included.

Example electrode compositions to which dopants can be added: metaloxides such as MnO₂, vanadium oxide, metal cobalt oxides, ternaryoxides, etc., plus one or more polymers (e.g., as a binder, ionicvehicle, or electronic conductor).

The present formulations may also be used with solid inorganicelectrolytes, combined with semipermeable or ionic soluble electrode orcollector compositions.

Experiments with Ionic Liquid Doping of Electrodes

Increasing electrolyte concentration and electrolyte conductivity, andin some cases, electrode ionic conductivity and suppression ofoutdiffusion of ionic electrolyte components into adjacent layers in alayered battery cell structure is of particular interest when theadjacent electrode and current collector layers may contain regionswhich have some solubility or provide a mobile path for diffusion ordrift of ionic species into these layers that can ultimately reduce theionic conductivity and performance of the cell. An example system wherethis occurs is a cell-based on a polymer electrolyte that contains oneor more mobile ionic species such as an ionic liquid, a metal salt, anorganic salt, a solvent, and/or an ionic complexing agent. When suchelectrolyte layers are surrounded by electrode or current collectorlayers that contain materials that have a finite solubility for theionic or solvating species in the electrolyte, these species and/ormaterials can diffuse into the other layers. Materials that have afinite solubility for these species and/or materials include activematerials and binder materials such as polymers.

In the following example, printed electrolyte, printed cathode, andprinted current collector cells with undoped cathodes and doped cathodesof various doping levels were compared in terms of their capacity fadeduring cycling (which may also include an element of time fading ofcapacity as cycling takes a finite amount of time). Electrolyteformulations were based on 1-butyl-3-methylimidazoliumtrifluoromethane-sulfonate, zinc trifluoromethanesulfonate, and PVDF-HFP(following WO12037171). Cathode formulations were as described in Table4 below. In this example, the current collector was not doped andcontained only carbon and PVDF-HFP.

TABLE 4 Cathode formulations in Top Cathode Architecture ExperimentAcros MnO₂ (MnO₂ dominated) - Acros - Acros - Acros - MnO₂ vendor seeS0033; no IL/salt 5% IL 10% IL 15% IL Density MnO₂ 5 5 5 5 MnO₂ Volume %83.49 78.65 74.34 70.48 PVDF Volume % 8.93 8.42 7.96 7.54 Carbon Volume% 7.57 7.13 6.74 6.39 IL/salt volume % 0.00 5.80 10.96 15.59 MnO₂ weight(g) 26.25 26.25 26.25 26.25 PVDF weight (g) 1 1 1 1 Carbon weight (g) 11 1 1 NMP (g) 25 25 25 25 Weight of IL/salt 0 0.5 1 1.5

All cell layers were printed by stencil printing with a 1 cm² activearea and dried in a convection oven (air). Devices were cycle tested inthe open air with an Arbin battery test system at 30 uA/cm² dischargecurrent density between 1.8V and 0.6V. Cycling results showed a decreasein cycle fade for the samples with electrolyte doping in the reductionin percentage cycle fade (e.g., the relative discharge capacity fromcycle 1 to cycle 2, and from cycle 1 to cycle 3). A trend of reducedearly discharge capacity face can be seen through the sample series9042_100 through 9042_400, which goes from no cathode doping (thecontrol sample set 9042_100) through increasing doping levels asdescribed in Table 5. This can be attributed to the reducedredistribution and diffusion of ionic liquid and or metal salt from theelectrolyte into the cathode. (no doping for 9042_100). Reduced %capacity loss with cycling was observed for the more heavily dopedcathodes

A Further Example of Printed Battery Structure(s)

Printed battery structures, including printed cathodes and, in somecases, printed anode structures were produced that demonstrate thepositive effects of doping in cathode and anode structures as comparedto undoped controls. The electrolyte chemistry followed WO12037171 ingeneral makeup, except that the ionic liquid used was1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and the Zn salt used was zinc(II)bis(trifluoromethanesulfonyl)imide (Zn TFSI). The ionic liquid andelectrolyte salt ratios relative to the PVDF-HFP content in theelectrolyte were the same as the ratios of ionic liquid and electrolytesalt to PVDF-HFP content in the electrodes, as described in Table 5.

TABLE 5 Experimental Variations: Sample Series Names 100 Series 200Series 300 Series 400 Series Cell Stack Base Cathode Doped Cathode BaseCathode Doped Cathode Descriptions on Zn Foil on Zn Foil and Anode onand Doped Anode on Substrate Anode Substrate Anode Stainless SteelStainless Steel Substrate High Purity Zn - High Purity Zn - StainlessSteel Stainless Steel Front Grid Front Grid Printed Anode Ink Undoped ZnInk Doped Zn Ink Z0002 Z0003 Printed Anode Process Stencil StencilPrinted Electrolyte Ink EMIM:TFSI EMIM:TFSI EMIM:TFSI EMIM:TFSI PrintedElectrolyte Process Stencil Stencil Stencil Stencil Printed Cathode InkUndoped Cathode Doped Cathode Undoped Cathode Doped Cathode Ink M0005Ink M0004 Ink M0005 Ink M0004 Printed Cathode Process Stencil StencilStencil Stencil Printed Top Ink C0002 C0002 C0002 C0002 CurrentCollector Printed Top Process Stencil Stencil Stencil Stencil CurrentCollector

The electrode ink formulations included (all values in grams):

PVDF NMP MnO₂ CARBON IL + Zn Salt M0004 2.005 33.333 52.533 2.006 3.133M0005 6.027 100.6 157.8 6.03 0 PVDF NMP Zn IL + Zn Salt Z0002 7.12*28.98 89.76 0 0 Z0003 2.373 9.66 29.92 0 3.71Results (Using Arbin Battery Test System)

As can be seen in FIG. 10, the doping of the electrodes increased thedischarge capacity of the cells. Comparing series 200 to series 100shows the impact of cathode doping on discharge capacity for cells withfoil anodes. An increase in capacity was observed for the doped cathodecase. Series 400 versus 300 compares cells with the doped printedcathode and doped printed anodes to cells with the undoped printedcathode and undoped printed anodes. In this case, a large performanceincrease was seen. The fact that the undoped printed anode cells (Series300) versus the foil anode controls (Series 100) were lower is possiblydue to loss of ionic liquid or metal salt form the electrolyte layerinto the binder of the undoped anode leading to depletion of ionicspecies in the electrolyte layer and reduced ionic conductivity. Ahigher average voltage throughout the discharge can also be seen in theSeries 400 cell versus the Series 300 cell.

Referring to FIG. 12, looking at discharge capacity over a range ofdischarge currents for sets of cells from the above experiment supportsthe overall trend for improved performance from cells having one or moredoped electrodes versus cells having otherwise identical undopedelectrodes. At lower currents, the improved performance of the dopedelectrodes is easily visible. At 500 uA/cm2 discharge currents, the datais more compressed, but the undoped anode and cathode still show thelowest performance.

It is important to emphasize that this concept extends not only toelectrodes but also to current collectors, specially printed and coatedcurrent collectors. Few others have worked with printed currentcollectors. Likely, the concept of including electrolyte doping toprevent diffusion, swelling, and function loss into current collectorsfrom the electrolyte and electrodes may be novel and useful sinceprinted conductors are typically metal particles in a matrix that mayhave solubility and/or permeability for the electrolytic materials thatshould remain in the active regions of the battery. Also, since it isadvantageous to dope the electrodes, there may be a problem of loss ofthose dopants to the next adjacent layer (i.e., the current collector).Typically, foil collectors are used in the battery industry.

Cross-linking of the dopants in the binder networks of the electrodesand collectors can stabilize the motion of these materials, preventingthem from transporting in or out of the cell, and thereby stabilizingtheir blocking effect on the outflow of ionic and solvating species fromthe interior layer(s) in the cell (electrolyte or electrodes).

Use of polymer-tethered counter-ion metal salts in printed and/orsolution deposition cells as a means to suppress out-diffusion of anionsfrom the electrolyte layer, an electrode or a current collector.

Inclusion of pH modifiers in the electrodes and/or current collectors toprotect those layers. It may be advantageous where a pH modifier, suchas a low pH buffer or acidic additive (e.g., a carboxylic acid, fattyacid, etc.) can help protect or stabilize Zn ions or collector metalsand suppress oxide formation and proton-based side reactions at oneelectrode or collector. However, that same modifier may be detrimentalat another electrode or at another location within the cell. In thisdisclosure, the pH modifier is placed at a particular layer or interfacein the cell. This can be achieved by incorporating it into ink to becoated or printed for that particular layer, or exposing the cell at theright point in the process to a liquid diffusion source for the modifieror a vapor-based source to cause a local modification.

The present doping approach may be used in the case where there areblends of ionic species in the electrolytes, and the doped layerscontain at least one component (up to all components) of that blend.

It may be advantageous for an ion transport-blocking layer to be dopedwith an ionic material that contains one ion (either cation or anion)that is also contained in the electrolytic layer, but that has adissimilar counter ion.

In the case of a diffusion/redistribution-blocking layer doped with adissimilar counter ion, when the dissimilar counter ion is a less mobilespecies, this can provide an anchoring effect, while maintaining thedesired ion-blocking effect.

Also included within the scope of the present disclosure:

-   -   The present doping approach can enhance ionic conductivity and        electrolytic activity in the electrodes and/or current        collectors, in addition to blocking redistribution of beneficial        species from the electrolyte layer and/or electrode to the        current collector.    -   The present doping approach can enhance ionic conductivity and        electrolytic activity in the electrodes, in addition to causing        swelling in the electrodes or in a current collector (which may        be printed).    -   The present doping approach can enhance ionic conductivity and        electrolytic activity in the electrodes, in addition to reducing        or avoiding the risk of delamination of layers in a cell or cell        battery stack due to swelling-induced stresses or the        redistribution of species to the interface between cell layers        and between cell and substrate or packaging layers. The presence        of these species can compromise the mechanical and electrical        bonding between battery layers.    -   The concepts in this patent application can apply to anode and        cathode layers, as well as their associated collectors.    -   It may be advantageous for the dopant in the electrode or        collector to contain an ionic material in which at least one of        ions is common with the electrolyte or adjacent layer, while the        other ion(s) in the electrolyte or adjacent layer are different,        as this may provide a diffusional barrier for the common ion,        but allow for other beneficial properties such as using immobile        other ions in the electrode or current collector that could be        less susceptible to redistribution and that may have other        beneficial roles in the electrode or current collector. This may        include polymer ions that also have desirable mechanical        properties in the electrode(s) and/or current collector(s).

Doping the anode may suppress unwanted shape change or dendriteformation by regulating the IL and/or electrolyte salt concentrationgradient at its interface with the electrolyte layer. Such shape changeor dendrite formation can cause premature failure or non-homogenousutilization of the electrode. A regulated concentration gradient (or alack of a concentration gradient) may affect and/or control the surfacekinetics of reactions (e.g., electrodeposition, or electrochemicalstripping of ions) at the anode surface.

Introduction and control of ionic species and their concentrationprofiles throughout the cell can be achieved through the inclusion ofthe species in different layer formulations prior to deposition.However, they can also be introduced or controlled through theapplication of electric fields to drive motion/transport and the speciesdistribution during cell fabrication, after fabrication, or during use.The magnitude of the electric fields that can be applied to the cell todrive motion/transport of ionic species along with their duration willaffect the motion/transport of the ionic species and therefore dictatethe distribution of these species through the cell and its layers. Forexample, a series of large electric field pulses, followed by a longduration of a low electric field, may allow more uniform concentrationdistributions of the ionic species through the cells and its layers.

External layers, including solid or liquid layers, can also be sourcesof the beneficial ionic, transport, or additive species to redistributeinto the active cell layers. These external layers could be provided byimmersion, printing of additional layers, spraying, or lamination of adonor layer. This donor layer may form part of an encapsulation barrierfilm, protection film and/or adhesive layer. Example adhesives includeacrylics, acrylic acids, polyethylenes, methacrylic acids, silicones,and hydroxyl-terminated silicones. Example buffer or packaging layermaterials include polyimides, polyesters, polyvinyl alcohols,polyethylenes, fluorinated ethylenes, polyvinylidene fluorides,polyvinylidene chlorides, and ethylene vinyl alcohols.

What is claimed is:
 1. A positive electrode ink for printing a positiveelectrode layer of an electrochemical cell over a positive currentcollector of the electrochemical cell, the positive electrode inkcomprising: a positive active material, comprising a metal oxide; apolymer binder, comprising at least one of polyvinylidene fluoride, acopolymer of polyvinylidene fluoride, a polyaniline, a polyether, apolyethylene oxide, a polyimide, a polyacrylate, a polyacryliccopolymer, a polyester, a polyester copolymer, or a polyvinylidenechloride; a conductive additive, comprising at least one of graphite,acetylene black, carbon nanotubes, or graphene; and a doping solution,comprising an ionic liquid and an electrolyte salt, the ionic liquid,comprising at least one type of cations selected from the groupconsisting of imidazolium, pyrrolidinium, tetraalkyl amine, andammonium, and also comprising at least one type of anions selected fromthe group consisting of trifluoromethane-sulfonate (triflate),bis((trifluoromethyl)sulfonyl)imide, triflate sulfimide,hexafluorophosphate, and tetrafluoroborate, the electrolyte salt,comprising at least one type of cations selected from the groupconsisting of zinc cations, aluminum cations, magnesium cations, andyttrium cations and also comprising at least one type of anions selectedfrom the group consisting of chloride, tetrafluoroborate (BF₄ ⁻),trifluoroacetate (CF₃CO₂ ⁻)trifluoromethanesulfonate (CF₃SO₃ ⁻),hexafluorophosphate (PF₆ ⁻), bis(trifluoromethylsulfonyl) amide (NTf₂⁻), and bis(fluorosulfonyl)imide (N(SO₂F)₂)⁻.
 2. The positive electrodeink of claim 1, wherein the ionic liquid comprises are imidazolium saltor a pyrrolidinium salt.
 3. The positive electrode ink of claim 1,wherein the ionic liquid comprises 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide.
 4. The positive electrode ink ofclaim 1, wherein the electrolyte salt comprises zinc(II)bis(trifluoromethanesulfonyl)imide.
 5. The positive electrode ink ofclaim 1, wherein the polymer binder comprises poly(vinylidenefluoride-co-hexafluoropropene).
 6. The positive electrode ink of claim1, further comprising a solvent.
 7. The positive electrode ink of claim6, wherein the solvent has a high boiling point of greater than 150° C.at 1 atm.
 8. The positive electrode ink of claim 1, wherein the metaloxide of the positive active material comprises one of manganese oxide,vanadium oxide, metal cobalt oxide, or a ternary oxide.
 9. The positiveelectrode ink of claim 1, wherein the metal oxide is manganese oxide.10. The positive electrode ink of claim 1, wherein the doping solutionis a separate ink part from the positive active material, the polymerbinder, and the conductive additive.
 11. The positive electrode ink ofclaim 1, wherein the conductive additive comprises graphite andacetylene black.
 12. The positive electrode ink of claim 1, wherein thedoping solution is mixed with the positive active material, the polymerbinder, and the conductive additive.
 13. The positive electrode ink ofclaim 1, wherein the ionic liquid or the electrolyte salt is at asaturation concentration in the positive electrode ink.
 14. The positiveelectrode ink of claim 1, wherein the positive electrode ink isconfigured for stencil printing.
 15. The positive electrode ink of claim1, further comprises a pH modifier, selected from the group consistingof a low pH buffer and an acidic additive.
 16. The positive electrodeink of claim 6, wherein the solvent is n-methylpyrolidone (NMP).
 17. Thepositive electrode ink of claim 6, wherein the solvent has a highboiling point of greater than 200° C. at 1 atm.
 18. The positiveelectrode ink of claim 1, wherein: the ionic liquid comprises1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; theelectrolyte salt comprises zinc(II) bis(trifluoromethanesulfonyl)imide;and the polymer binder comprises poly(vinylidenefluoride-co-hexafluoropropene).
 19. The positive electrode ink of claim18, wherein the metal oxide is manganese oxide.
 20. The positiveelectrode ink of claim 15, wherein the pH modifier comprises the acidicadditive selected from the group consisting of a carboxylic acid and afatty acid.